1. Characteristics of the cured material 

The efficiency of a UV lamp depends on how easy it is for the photons emitted by the lamp to enter the curable material to trigger photoinitiated molecules. UV curing depends on the collision of photons with molecules. Light can induce uniform diffusion of molecules through the material. In addition to the properties of the UV light source, the cured substrate has optical and thermodynamic properties, which interact with the radiant energy and have a significant impact on the curing process.   

2. Spectral absorbance

Light energy is how much the ink absorbs into wavelengths over an increasing thickness. The more energy absorbed near the surface, the less energy the deeper layers get. But this situation varies with wavelength. The total spectral absorbance includes all effects from photoinitiators, unimolecular species, oligomers and additives including pigments.   

3. Reflection and Scattering

Compared with absorption, light energy is more redirected by ink, resulting in reflection and scattering, which is generally caused by the matrix material or pigment in the curable material. These factors reduce the UV energy reaching the deep layer, but improve the curing efficiency at the reaction site.   

4. Infrared absorption rate  

Temperature has a significant impact on the rate of the curing reaction; although the temperature rise during the reaction is also relatively effective, the radiation from the UV lamp is the fundamental source of surface heat, and excessive temperature rise will affect the curing process. one of the important limiting factors.   

5. The meaning of spectral absorption  

Substances absorb light differently depending on the wavelength. Obviously, short UV wavelengths (200~300nm) will be absorbed at the surface without reaching the bottom layer at all. Even a photoinitiator absorbs the range of wavelengths it is sensitive to, preventing that wavelength from reaching the deep photoinitiated molecules. A photoinitiator is suitable for clearcoat coatings, but may not be a suitable choice for inks. For inks, longer wavelength (365nm) photoinitiators are a better choice.   

6. The important role of wavelength  

Most UV curing involves the simultaneous operation of two ranges of wavelengths. Short wavelengths work on the surface layer and long wavelengths work on the deeper layers of the ink or coating. This theorem is a consequence of the fact that short wavelengths are absorbed at the surface and cannot reach the deeper layers. Insufficient short-wave curing can result in a tacky surface; insufficient long-wave energy can result in poor adhesion to the print. The most basic mercury lamp emits energy in these two ranges, but its strong emission at short wavelengths makes it especially suitable for thin ink layers. Highly absorbent materials, such as adhesives and screen inks, are formulated for long-wave curing using long-wave photoinitiators. The lamps used to cure these materials, which contain halides and mercury, emit more light in the long-wave UV, and these long-wave lamps also radiate some short-wave energy, which is sufficient for surface curing.