What are the six additives commonly used in UV coatings?
UV cationic and UV free base materials are very different, but the overall composition is similar. The cationic system is mainly epoxy materials, but the ordinary bisphenol A epoxy reaction speed is slow, with more applications of alicyclic epoxy / oxetane materials; free radical system commercialization is now very mature, with epoxy / polyester / polyurethane modified acrylate materials can provide more choice of solutions.
UV cationic systems have fewer raw material options than free radical systems, and low viscosity alicyclic epoxy resins are the main polymers. Take alicyclic epoxy resins as an example.
TTA21 of various purity specifications is the most dominant product in the UV coating industry. As the application of cationic UV coatings/applications continues to grow significantly, it is foreseen that the amount of alicyclic epoxy resins represented by TTA21 will increase.
In the specific product applications of inks/coatings, in addition to both needing UV light to provide curing energy, the two systems reflect major differences in performance performance and reaction characteristics.
1. Oxygen-blocking effect
UV cationic system does not have the effect of oxygen-blocking, but more afraid of water, moisture will affect the curing efficiency of cationic system; UV free radicals on the contrary, by the oxygen-blocking influence.
2. Substrate adhesion
Usually in the more difficult to adhere to the surface of the substrate, such as glass / metal / high-density plastic, UV cation than UV free base has better adhesion performance.
3. Volume shrinkage rate
UV free radical system formulation curing shrinkage rate is generally above 10%, while UV cation system can control the shrinkage rate of 1-3%, is a good solution to solve the volume shrinkage.
4. Dark curing characteristics
UV cation system can continue to react to the inner layer after stopping the light source irradiation, to complete the material after curing, this is the dark curing characteristics, very suitable for thick coating applications, heating the cation after curing speed is significantly helpful; UV free radical is a stop-and-go reaction system.
5. Contact safety
UV cation system reaction degree is close to 100%, safety can be REACH / FDA testing certification, can be used in food packaging and other related fields.
6. Light curing speed
In general the UV free radical system curing speed than the cationic system, affected by oxygen-blocking products cationic surface drying will be faster, but the actual drying speed is not as fast as the free radical, you can promote the reaction by heating, and eventually can reach a very good degree of completion.
Formulation notes
UV cation system can be mixed with UV free radical system in any proportion, called UV hybrid system, can improve the relative curing speed of UV cation and UV free radical shrinkage, affected by oxygen barrier and other shortcomings, the same film thickness of the system curing energy difference is not large.
UV cation system is to rely on the initiator generated by Lewis strong acid to do the active point of the ring-opening reaction, the formula will commonly affect the initiator activity of the material is mainly azo organic pigments (can be modified to do protection), and free radicals mixed with TPO/819/907 and other structures containing P, S and other elements of the initiator, and similar to 115 multi-level amine.
Humidity on the UV cationic system curing influence, control the ambient humidity within 50% is appropriate; while heating will speed up the reaction speed.
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