1 Waterborne urethane acrylate

Water-based UV-curable urethane acrylate (WPUA) replaces the reactive diluent monomer in traditional UV-curable coatings with water, and solves the problems of irritancy, environmental pollution and unsafeness caused by volatile organic components.

Therefore, in recent years, it has received extensive attention and rapid development. According to different emulsification methods, it can be divided into external emulsified type and self-emulsified type. The external emulsified type uses an external emulsifier to disperse the UV-cured PUV resin in water under the action of high shear force.

The self-emulsifying type introduces a hydrophilic group on a hydrophobic polyurethane main chain and then disperses it in water. The self-emulsified type can be classified into an anionic type, a cationic type, and a nonionic type depending on the introduction of a hydrophilic group.

 
WANG Zhiming et al. used three steps of toluene diisocyanate (TDI), polyethylene glycol (PEG), dimethylolpropionic acid (DMPA), triethylamine (TEA) and hydroxyethyl methacrylate (HEMA). The PUA polymer is synthesized (as shown in Figure 3), and water acts as a chain extender and dispersant during the mixing of the modified prepolymer.


XU Heping et al. used isoflurane diisocyanate (IP-DI), polyether polyol (NJ-210), dimethylolpropionic acid (DMPA) and hydroxyethyl methacrylate (HEMA) to pass in situ anion The urethane acrylate oligomer is obtained by emulsification.

The effects of reactive diluent BA/TPGDA and photoinitiator Darocur 1173 on UV curing time and film properties were investigated.

By measuring the mechanical properties, solvent resistance and gel content of the UV-PUA film, the UV-PUA film has the best solvent resistance when the ratio of BA and TPGDA is 5:5.


In addition, as the ratio of BA and TPGDA increases, the surface drying time increases. When the content of Darocur 1173 is 4%, the gel content reaches a maximum and the surface drying time reaches a minimum.

Zhang Wenjun et al. used photopolymerization and surface active properties of vinyl benzene sulfonate to catalyze the reaction of acrylic acid with pentaerythritol to synthesize a mixture of pentaerythritol acrylates with different hydroxyl contents.


Further, it is reacted with a polyurethane prepolymer prepared from isophorone diisocyanate and polyethylene glycol to obtain a urethane acrylate.


Studies have shown that when the amount of catalyst is 4% and the molar ratio of pentaerythritol to acrylic acid is 3.2:1, the comprehensive performance of waterborne urethane acrylate UV cured film is the best.


Yang Fan et al. used isophorone diisocyanate (PDI), 2,2-dimethylolpropionic acid (DMPA) and polyethylene glycol 400 (PEG400), hydroxyethyl acrylate (HEA), pentaerythritol triacrylate, etc. A difunctional aqueous urethane acrylate (WPUA2) and an aqueous hexafunctional urethane acrylate (WPUA6) oligomer were synthesized.


Studies have shown that compared with WPUA2 UV-curable film, the use of polyfunctional WPUA6 can increase the gel fraction of PUA cured film by more than 20%, water absorption by 30%, mass loss by 10%, and decomposition temperature by 82 °C.


While the combination of UV curing technology and waterborne coating technology brings advantages, there are also some disadvantages such as water to inhibit the polymerization of free radical polymerization.


At the same time, it takes a lot of energy to remove water, and it is difficult to cure a complex shape substrate, and it needs to be solved by various modification methods.