Jin Who Hong

The effects of silica nanoparticles on the photocuring behaviors of UV-curable polyester acrylate-based coating systems

ConclusionsThe photocuring behaviors of UV-curable PEA-based coating systems with and without silica nanoparticles have been studied by photo-DSC, UV-visible spectroscopy, and FTIR spectroscopy. Photo-DSC analysis revealed that as the concentration of silica nanoparticles was increased up to 5 wt%, the exotherm, ultimate percentage conversion, and cure rate increased gradually, whereas they decreased above 10 wt%. This result was confirmed by FTIR spectroscopy analysis and indicated that the presence of silica nanoparticles at below 10 wt% accelerated the cure reaction and cure rate of the UV-curable PEA-based systems due to the synergistic effect of silica nanoparticles as an effective flow or diffusion-aid agent during the photopolymerization process and by lengthening the path of the UV light by partial scattering or reflection. However, a decrease in photopolymerization reactivity occurred when the silica content was increased above 10 wt%, which is attributable to aggregation of silica nanoparticles due to their high surface energy.

Dual-curable acrylic pressure-sensitive adhesives based on UV and thermal processes

Several dual-curable acrylic pressure-sensitive adhesives (PSA) were synthesized by the radical polymerization of acrylic monomers containing benzophenone, hydroxyl, and alkyl groups. The optimum extent of UV-induced cure was determined by varying the content of the benzophenone groups (the photoinitiator) from 0.5 to 1.5 wt%. The weight average molecular weight of the polymers obtained ranged from 300,000 to 700,000 amu. The coated pressure-sensitive adhesives were cured either by short UV exposure to induce the grafting of acrylic polymers, or by heating for 6 h at 60 °C to promote the reactions between the polyisocyanates and hydroxyl groups. The dual-curing behavior was determined by monitoring both processes quantitatively by infrared spectroscopy. The developed dual-curable acrylic pressure-sensitive adhesives were found to compensate for the limitations in UV-induced curing of thick coatings.

Surface and dielectric properties of oriental lacquer films modified by UV-curable silicone acrylate

In order to achieve an oriental lacquer (OL) film with a thick consistency, UV-curable silicone acrylate (SA) was added to OL by a dual curing process. The addition of 5 wt% UV-curable SA to the OL formulation enabled the preparation via a single drying step of a 77 μm-thick film exhibiting excellent surface properties. FTIRATR was used to investigate the effect of UV-curable SA on the behavior of film formation during curing, and the relaxation behavior of the produced films was investigated by dielectric spectroscopy. Dielectric properties were measured in the frequency range 10−2–105 Hz at various temperatures between −100 and 200 °C. The results demonstrated that OL modified by UV-curable SA has a higher glass transition temperature and stronger secondary relaxation at a lower temperature than the conventional OL system. The OL film modified with UV-curable SA was presumed to be harder at the surface and tougher than conventional OL film.

Photostabilization and Cure Kinetics of UV-Curable Optical Resins Containing Photostabilizers

The photostabilization and cure kinetics of UV-curable, optical resins containing various formulations of photostabilizers were investigated to determine the system with the highest cure conversion and durability. Photo-DSC analysis revealed that increasing the concentration of a UV absorber (UVA) decreased both the cross-link density and the cure rate due to competition for the incident photons between the photoinitiator and the UVA, whereas including a hindered amine light stabilizer (HALS) hardly affected either the cure conversion or the cure rate due to its very low absorption of 365 nm. This result was confirmed by FTIR-ATR spectroscopy and UV-visible spectroscopy analyses. QUV ageing experiments showed that the cure conversion and durability were the highest for the UVA/ HALS formulation at a ratio of 1 : 2, which is due to their synergistic action.