Yang-Bae Kim

UV-curable polyurethane dispersion for cationic electrodeposition coating

UV-curable polyurethane dispersions were prepared for cationic electrodeposition coating. Methacrylate groups were introduced to the ends of the polyurethane main chains by a sequential condensation reaction. The neutralized polyurethane polymer containing photoinitiator with or without multifunctional acrylate (pentaerythritol triacrylate, PETA) could be dispersed into a stable dispersion without any phase separation. The size of the particles in these polyurethane dispersions was approximately 100 nm, and increased slightly with the incorporation of PETA. The electrodeposition process was used to introduce UV-curable polyurethane dispersions into the nickel-plated plastic substrate. The drying process of the electrodeposition film was completed in 6 min under infrared radiation, which is comparable to the time taken when using a conventional UV coating system. Studies of the kinetics using real-time FTIR and photo-DSC revealed that the cross-linked films containing PETA gave a higher conversion rate than those without PETA, resulting in better resistance to methyl ethyl ketone.

Epoxy-acrylic microgels in electrodeposition coating films

Abstract Epoxy-acrylic microgels (EAM) have been prepared via an aqueous dispersion polymerization of a mixture of acrylic monomers in the presence of the cationic soap with the quaternary ammonium salt groups and 2,2′-azobis(2-methylpropionitrile) (AIBN) as an initiator. The prepared microgels have a bimodal particle size distribution of 10 and 52 nm, and consist of a cross-linked acrylic polymer and cationic epoxy resin. Rheological data from the pendulum type rheovibron show that the presence of the spherical microgels in electrodeposition paint perturbs the flow of the surrounding fluid in a low shear field. A scanning electron microscope (SEM) showed that edge protection (%) at a knife blade increased proportionally with the amount of the microgel in the coating formulation. The microgels also provided excellent corrosion resistance; the cured film containing more than 7% microgels was free of rust spots after 168 h of the salt fog spray test. These results lead to the conclusion that EAM has a remarkable ability to perturb the thermal flow during the curing process and can be used in electrodeposition coating formulations to provide edge protection.

Photocure kinetics and control of LC microdroplets for acrylate-based polymer dispersed liquid crystal with different methacrylate contents

AbstractThis paper reports on the relationship between the photocure kinetics and the morphological properties of UV-curable acrylate-based polymer dispersed liquid crystal (PDLC) systems with the various 2-ethylhexylacrylate (2-EHA) and 2-ethylhexylmethacrylate (2-EHMA) contents using photo-differential scanning calorimetry (photo-DSC), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). Photo-DSC analysis using an autocatalytic kinetics model demonstrated that the cure extent and cure rate gradually decreased and then leveled off as the concentration of 2-EHMA increased up to 25 wt%, which was well confirmed by using FTIR spectroscopy. The morphological observations revealed that increasing the 2-EHMA content increased the size of the LC droplets within the acrylate-based polymer matrix. Notably, there was a marked increase in the number of LC droplets larger than 10 μm in PDLC composites containing more than 20 wt% 2-EHMA, suggesting that the addition of more than 20 wt% 2-EHMA to the acrylate-based PDLC compounds is not desirable. The presence of 2-EHMA clearly affected the photocure behaviors of acrylate-based PDLC compounds, which interestingly means that the slow reactivity of methacrylate monomer could be simply used to control the phase separation rate and the microstructures of LC droplets of acrylate-based PDLC systems.