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Meaning of Ultraviolet Ray Hardening
Ultraviolet ray (UV) hardening is the method of using prepolymers, monomer, and light polymerization starting dose to form ultraviolet ray UV hardened resin, radiating light rays (a few seconds ~ a few tens of seconds) having 200~400nm wavelength, and have it hardening in a short span of time.

A. UV rays normally pertain to light rays (electromagnetic waves) with wavelength 100 ~ 400nm. Please refer to the figure below. If the light (electromagnetic wave) and the wavelength are inversely proportional, energy E will increase.

The UV ray wavelengths used by UV ray hardening are mainly the 254 nm and 365 nm of the emission ray spectrum of mercury.
Property of 254 nm UV ray is : Although it has great amount of energy, it is difficult to reach the interior of the resin. The energy of 365 nm UV ray is smaller, but it can better penetrate the interior of the UV ray resin.

B. UV ray resin is normally formed from prepolymers, monomers, light polymerization starting dose, and additives. Each has a function as indicated below.

Prepolymers Main ingredient of UV ray hardening resin
Monomer Reactive diluting agent used to adjust resin's viscosity
Light polymerization starting dose A compound which starts light polymerization reaction upon being radiated by UV rays
Additives Filling agents, coloring agents, molding agents

C. The summary of light polymer reaction is: If radiated by UV rays, light polymerization starting dose will become free radicals. This reaction is close to the polymeric double union (unsaturated radicals) of prepolymers and monomers, letting the double union part become activate and consequently form a chain union. Please refer to the figure below.

Light polymerization reaction is hindered by the oxygen in the air. Hence, to handle UV ray hardening resin surface in contact with air within a short span of time, Type B light focusing lens having 254 nm with higher ultraviolet ray intensity is more effective. Also, if the film thickness of the solidified resin is thicker (above 1mm), Type C light focusing lens having visible light of 405 nm and 436 nm is more effective. Please refer to the figure below.