UV curable adhesives are one-component materials, they can cure quickly after UV exposure to high-strength materials. But during UV adhesives production, there are issues like curing bad, not enough depth curing, or surface sticky. Then how to make good UV curable adhesives?
To make good UV curable adhesives, in other words, is to improve the performance of the adhesive. There’s evidence showing the adhesive performance is due to curing depth. While the curing depth is due to many reasons. Like composition, types of photoinitiator, temperature, wavelength, the bandwidth of the curing light, light intensity, or exposure duration. It is also a guide for applications.
Light intensity is one of the factors of the UV adhesives performance. After increasing UV intensity, curing depth is well strengthened.
It cures the surface very quickly at wavelength 365nm. The wavelength at 385nm or higher can cure materials uniformly, and the light can penetrate and cure thicker sections of the adhesive. In conclusion, the visible range is closer to the wavelength, the easier it is to cure.
After increasing the opacity or darkening the color, curing depth is reduced.
In general, there are two types of photoinitiators. The type I of photoinitiator is the Norrish type, it generates free radicals by photoinitiator cleavage; Furthermore, photoinitiators extract hydrogen from co-initiators (amine synergists). The type II photoinitiators generate free radicals. How to choose Photoinitiators types? You can select photoinitiators according to the type of UV lamp. As the spectral output has to fit the optimal range for UV curing. See what photoinitiators we can select for LED lamps.
After increasing photoinitiator concentration, curing depth is well strengthened. However, the strength is reduced after reaching optimum concentration. So photoinitiator concentration is also related to curing depth.
The thinner the material thickness is, the better for curing. The colored ink can obtain sufficient curing performance in the range of 10~12um thickness. If more than 15um thickness, it may cause bad curing. While for varnish inks, even with extremely thickness exceeding 100um, there is no problem with curing.