The "invisible killer" of UV curing: mechanism analysis and solution of oxygen inhibition
As one of the most important green manufacturing technologies in the 21st century, ultraviolet curing (UV curing) technology plays a key role in many fields such as printing, electronics, automobiles, and medical treatment. However, oxygen inhibition is like an "invisible killer", which seriously restricts the performance and application expansion of UV curing technology.
The most direct manifestation of oxygen inhibition is the "stickiness" of the coating surface: after UV light irradiation, the inside of the coating has been completely cured, but the surface remains sticky, and the expected curing effect cannot be achieved. This "inconsistent" phenomenon not only affects the appearance quality of the product, but is also likely to cause subsequent processing difficulties, product performance degradation, and even the scrapping of the entire batch of products.
From the perspective of product performance, oxygen inhibition will lead to a large number of unstable oxidation structures on the surface, causing defects such as yellowing and pinholes, which seriously affect the service life and reliability of the product.Due to its unique triplet ground state structure, the reaction rate of oxygen molecules with free radicals is 4-5 orders of magnitude higher than that of normal polymerization reactions, which is the fundamental reason for the oxygen inhibition phenomenon.
Studies have shown that through comprehensive measures such as inert atmosphere protection, formula optimization, and process improvement, oxygen inhibition can be effectively suppressed and UV curing efficiency and product quality can be significantly improved.
1. Physical barrier: Floating wax method and coating method.
2. Light intensity: A simple way to reduce oxygen inhibition is to increase the light intensity, which will cause the initiator to form a higher concentration of free radicals, which will quickly combine with dissolved oxygen and reduce its concentration.
3. Light source: Continuous irradiation UV flash technology can produce short and high-intensity ultraviolet radiation pulses, thereby generating extremely high concentrations of free radicals.The vacuum ultraviolet light (such as 172 and 222nm) emitted by the excimer lamp can only cure ultra-thin coatings of 1-2μm due to the low transmittance of vacuum ultraviolet light; curing in this band does not require a photoinitiator, the corresponding initiating free radical concentration is very low, and significant ozone is produced when the reaction is carried out in the air.
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