Selective Glaze for Last Line Visible Thermal Head

Abstract

A thermal head in which the last line is visible allows characters to be viewed as soon as they are printed. The thermal head is constructed with a selective glazed layer and heat sources, which are formed at the edge of a ceramic substrate. The selective glazed layer must be smooth and flat, even at the edge, for heat sources to be formed on it. Selective glaze characteristics were studied using PbO-B₂O₃-SiO₂ and B₂O₃-SiO₂ glazing materials to realize the last line visible thermal head. Several commercially available gold conductors were screen printed on fine grained alumina substrates. Wettability, levelling characteristics and flatness at the edge of the selective glaze on each gold conductor were examined. Dependence of their characteristics on firing conditions were also examined. A combination of PbO-B₂O₃-SiO₂ glass and fritless gold conductor provides a smooth and flat glaze surface even at the edge, and experimental results show that PbO-B₂O₃-SiO₂ glazing material has the most suitable characteristics for a last line visible thermal head. A last line visible thermal head was formed using PbO-B₂O₃-SiO₂ glazing material. The selective glazed layer was formed over the thick film circuits of gold for the power supply, which were screen printed on a fine grained alumina substrate. Ta₂N thin film for resistive heat sources was formed at the edge of the glazed layer. The thermal head provides good print quality and can print 20 characters/line at 5 lines/sec with a resolution of 2.7 dots/mm.