The development direction of photoinitiator focuses on hybrid type, visible light type, water-based type, macromolecule type and so on, as well as the use of dual curing mode, by the icing on the icing effect.
1, free radical - cation hybrid photoinitiator
Free radical r & D system has fast curing speed but large shrinkage. And cationic light curing volume shrinkage, strong adhesion, curing process is not oxygen resistance polymerization, reaction is not easy to terminate, "post-curing" ability is strong, suitable for thick film light curing, but the curing speed is slow. Combining the advantages of the two, the free radical and cationic photoinitiator are mixed into a hybrid system, which can not only achieve free radical polymerization but also achieve cationic polymerization. More satisfactory results can be obtained when two or more
Photoinitiators are used together.
2, visible light initiator
Fluorodiphenyl titanium (Irgacure 784) and bisfluorophenyl titanium (pentafluorophenyl) have outstanding photoinitiation activity, storage stability and low toxicity. Their absorption wavelengths have been extended up to 500nm, with large absorption in the visible region, which is particularly effective for visible light initiated polymerization curing of acrylates. And because of the photobleaching effect of titanium ceng light, the film yellowing index is small; And the depth of curing is good, which is conducive to the thorough curing of thick film. In acrylate system, the photoinitiation efficiency of 0.2% is 2~6 times higher than that of 2%Irgacure651.
3. Water-based photoinitiator (WSP)
Aqueous photoinitiators were prepared by introducing functional groups of ammonium salt or sulfonate into common photoinitiators and making them dissolve with water. The main types are aryl ketones, including diphenylketone derivatives, thioxanthanone derivatives, alkyl aryl ketone derivatives, benzoyl derivatives, etc.
4. Macromolecule photoinitiator
The ordinary photoinitiator is introduced into the macromolecule chain, and it becomes the macromolecule photoinitiator. It has good compatibility with the resin, does not migrate after curing, is not easy to volatilization, and reduces the odor. Macromolecular photoinitiators can be divided into four types: side chain cleavage type, main chain cleavage type, side chain hydrogen capture type and main chain hydrogen capture type. The side chain cleavage macromolecular photoinitiators are relatively successful at present.
5, double curing
It is the combination of light curing and other curing methods, complement each other, highlights the advantages, has low temperature rapid curing, excellent stability, can avoid separation not curing, get good mechanical properties and stable size of the curing. The development of dual curing system shared by light curing and other curing methods is effective in overcoming the weakness of light curing adhesives, expanding the application range and improving the competitiveness. Other curing methods: heat curing, moisture curing, oxidation curing, anaerobic curing, etc.
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