UV curing is a process in which ultraviolet (UV) light rapidly cures adhesives, coatings, and inks. One of the key factors in achieving a successful UV cure is the selection of the right UV spectrum. This article will discuss the different UV spectra and how to achieve a full cure in thin or thick layers of adhesive using UV-LED technology.
Two main types of UV spectra are used in light curing: Near UV (NUV) and deep UV (DUV). DUV has a wavelength range of 100 to 300 nanometers (nm). The printing or packaging industry applies this spectrum to cure inks or thin coatings and create tack-free surfaces with photosensitive material formulated to work with conventional mercury discharge or excimer lamps.
NUV covers the spectral range between 300 and 400 nm. It can penetrate deep into the adhesive, allowing for a full cure even in thick layers. This property is essential for many UV curing applications in the automotive, electronics, medical, and optics manufacturing domains. And some challenging cases (extra thick adhesive layers) might require extending the curing spectrum well into the visible (VIS) range up to 450 nm. High-power UV-LEDs featuring a central wavelength (CWL) around 365, 385, 405, and 435 nm are the preferred light source for NUV curing applications.
When selecting a UV spectrum for curing, it is crucial to consider the thickness of the adhesive layer. Light with longer wavelengths can travel deeper into thick layers of adhesive, resulting in a full cure. Shorter wavelengths are preferable for surface curing applications. However, recently introduced light-curable products are often optimized for UV-LED light sources and do not necessarily need DUV radiation to achieve tack-free surfaces.
It’s also important to note that depending on the type of adhesive and the application, different UV spectra might be necessary to achieve a full cure. In some cases, you may need a combination of lower and higher spectral ranges to get the desired results. For example, there are applications that initiate the curing process with radiation around CWL 405 or 435 nm, followed by 365 nm to complete the (surface) cure.