The development direction of photoinitiator focuses on hybrid type, visible light type, water-base type, macromolecular type, etc., as well as double curing method, which has been greatly improved.
1. Free radical - cationic hybrid photoinitiator
Free radical research and development system curing speed is fast, but shrinkage is large. In contrast, cationic light curing is characterized by reduction in volume and strong adhesion, and the curing process is not blocked by oxygen. The reaction is not easy to stop. By combining the advantages of the two, free radical and cationic photoinitiator are mixed into a hybrid system, which can realize cationic polymerization of the tourists by free radical polymerization. When two or more photoinitiators are used in combination, more satisfactory results can be obtained.
2. Visible light initiator
Irgacure 784 and double (pentafluorophenyl) titanium alum have outstanding photoinitiatory activity, storage stability and low toxicity, and its absorption wavelength has been extended to 500nm. It has relatively large absorption in the visible region, and is especially effective for the visible light induced polymerization curing of acrylate. Due to the photobleaching effect of titanium alum, the film yellowing index was small. And the deep curing is good for the complete curing of thick film. Fluorinated diphenyl titanium peroxide photoinitiator is active. In the acrylate system, the photoinitiator efficiency of 0.2% is 2~6 times higher than that of 2%Irgacure651.
3. Water-borne photoinitiator (WSP)
The ammonium salt or sulfonate functional group was introduced into the ordinary photoinitiator, which was dissolved in water. The main types are aromatic ketones, including diphenyl ketone derivatives, thioxanthrone derivatives, alkyl aromatic derivatives and benzoyl derivatives.
4. Macromolecular photoinitiator
When the ordinary photoinitiator is introduced into the macromolecular chain, it becomes a macromolecular photoinitiator, which is compatible with the resin. After curing, it does not migrate and is not volatile, thus reducing the odor. Macromolecular photoinitiators can be divided into four types: side chain cracking type, main chain cracking type, side chain hydrogen capture type and main chain hydrogen capture type.
5. Double curing
In other words, the combination of light curing and other curing methods can complement each other, and the advantages are prominent. With low temperature and rapid solidification, excellent stability can be achieved, which can avoid separation of unsolidified materials and obtain curing materials with excellent mechanical properties and stable size. The development of dual curing system, which is Shared with other curing methods, is effective in overcoming the weakness of curing adhesive, enlarging the application range and improving the competitiveness. Other curing methods: thermal cure, moisture cure, oxidation cure, anaerobic cure, etc.