Hello, everyone, this article shares with you the impact of the distance between [UVLED light source] and the substrate. The radiation spectrum produced by traditional mercury lamps is wide, in which the radiation amount in the ultraviolet region is very significant, especially in the UVC, UVB, UVA and UVV regions. This spectral width allows the selection of the right photoinitiator based on the type and intensity of the light source and the type of substance in the formulation to optimize curing of acrylate-based inks, coatings, adhesives, sealants and composites to block or absorb UV light.
These traditional low-pressure mercury lamps radiate ineffective curing ultraviolet rays accounting for 70% to 75%, the most is high-energy infrared light, they can produce a lot of heat. A typical mercury lamp requires a large flow of air to keep it cool and, therefore, requires additional energy consumption. Such high flow rates make it impractical to use inert gases to improve surface curing properties. (Expensive inert gases are constantly being used up as the air cools.)
In the past 10 years, great progress has been made in generating the right amount of high-flux intense ultraviolet light sources with light-emitting diodes. For UV LED technology, there are now many commercial uses that do not require the use of large amounts of flowing air, and the reduced cost can be more widely used in thermal substrates, thus providing more economical UV curing performance. (When water cooling is used in high output systems >4 W/cm, energy savings are estimated to be up to 50% compared to typical mercury lamp systems 1,2.) Other advantages include a compact process with an “on and off”, no preheating required, and a longer lasting UV light source (20,000 hours vs. 2,000 hours).
UV LED light sources are described as non-focused systems, and tests are conducted to investigate the effect of the distance between the light source and the substrate on the “reactivity” (inferred from the reciprocating friction of the solvent).
The distance from the substrate between 4 and 8 mm can be seen to make a difference, but the reactivity is not further reduced at longer distances. The improved curing at a distance of 4 mm may also be attributed to the higher temperature at that distance, which is 110 ° C compared to 60 ° C at 8mm. Because of the grid, shorter distances cannot be achieved.
Other parameters considered are the effect of film thickness/mass and stabilizer on the reaction. Tests were carried out on coatings from 6 to 80 microns thick, and the results proved that there was little difference in curing. One explanation may be that sufficient curing requires a high concentration of photoinitiators and a strong permeability of light with a wavelength of 395 nanometers to overcome the surface curing inhibition commonly seen in conventional systems. The thickness of the film is less than 6 microns, which shows a good surface curing effect. Up to 4% in-tank stabilizers were tested in varnish formulations and found to have no effect on curing speed.
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