Sang-ki Chun

Characterization of the optical properties of silver nanoparticle films

To understand the collective properties of nanoparticles, it is necessary to control the particle size, spacing and ordering. Here we describe the chemical synthesis of well-controlled silver nanoparticles, the wet coat preparation and the optical properties of its film. The light incidence angle and polarization dependency of the resonant spectra show distinctive surface plasmon resonance extinction peaks for isolated particles and the coupled modes of neighbouring particles. Furthermore, we discuss the thermal treatment and dielectric surrounding effects on the optical properties of silver nanoparticle film.

The effect of shear force on ink transfer in gravure offset printing

This paper asserts that shear force plays an important role in the printing mechanism of gravure offset line printing. To that end, a theoretical printing model showing shear force dependence on the printing angle is proposed. The decrement of the internal angle between the printing direction and the pattern-line direction increases shear force, thereby enhancing the amount of transferred ink in the off stage. A printing experiment using pattern-line widths of 80 µm and 20 µm shows the angle dependence of the line width, thickness and amount of transferred ink, reflecting the effect of shear force. The effect of the internal angle on cross-sectional differences in lines with a width of 20 µm and with angle variation is greater than that in lines with a width of 80 µm, which corresponds with the theoretical prediction that shear force has greater influence on a narrower line. The strong correlation between the experimental data and the theoretical model supports the validation of the theoretical model.

Reliability of gravure offset printing under various printing conditions

This paper focuses on the reliability of gravure offset printing and presents a mechanism on how the width of the printed line increases on repeated printings. Of the various printing process parameters, such as the resting times between doctoring, off, and set, printing velocity, printing pressure, and so forth, we investigated the effects of printing velocity, printing pressure, and blanket’s thickness on the reliability of gravure offset printing. As the printing velocity increases, the reliability of gravure offset printing also increases. This is because the actual contact time between ink and blanket decreases, resulting in less solvent absorption into the blanket. Printing pressure does not have much influence on reliability. Even though some change was observed, it was within the range of experimental error. Under sufficient printing pressure, this observation implies that the more important factor as regards the absorption model is time rather than pressure. As the thickness of the blanket increa...

Resistivity transition mechanism of silver salts in the next generation conductive ink for a roll-to-roll printed film with a silver network

As the small size display market rapidly expands with the advent of smart phones and tablets, the industrial demand for a low cost transparent conductive film instead of an ITO sputtered one has expedited the development of a roll-to-roll printed one with a low temperature processable and highly conductive ink. The conventional conductive ink based on metallic nanoparticles capped with a polymeric dispersant, however, has difficulties in achieving high conductivity at a low curing temperature due to the unwanted residue of a polymeric dispersant. Therefore, a new kind of conductive ink was developed, where a silver salt replaces the role of a polymeric dispersant and also enriches the overall metallic content. The key to this new generation of conductive ink leans on the selection of a low temperature processable silver salt and the selection process of silver salts was on the basis of their thermogravimetric thermograms with the common belief that the thermogravimetric thermogram of a silver salt is coupled with its resistivity transition and final resistivity. In contrast to this common belief, our results show that the thermogravimetric behaviours of silver salts have little influence on their resistivity transition and final resistivity. With our comprehensive studies using various isomeric silver salts, we here suggest that the more persuasive and leading factors in determining the resistivity transition behaviour of a silver salt are stack integrity, phase transition, and the exothermic band in the differential scanning calorimetric thermogram. The next generation conductive ink with the most suitable silver salt was gravure-offset printed on a transparent and flexible film. Its sheet resistance after being cured at 150 °C is as low as 1 Ω □−1 with the line width of 20 μm and the optical transmittance of 85% and above.