| 摘要 |
PURPOSE:To make it possible to entrust a user with a matter of making a part or whole, which is invisible at the time of recording, visible by post-treatment, by using a pH indicator or discoloring dye as a color forming agent while using a pH controller in a coloration aid and combining said color forming agent with said coloration aid. CONSTITUTION:Solid printing is applied to the entire surface of high grade paper by a gravure printing press using ink containing phenolphthalein as a color forming agent and paraffin wax is thickly applied to the printed surface of said high grade paper to form thermal recording paper. A part of the color forming layer is penetrated in the base paper 1 and the recessed part 4 of a heat-sensitive part by a signal has the same hue as the other part and, therefore, a thermally recorded pattern is usually invisible by the naked eye. When a coloration aid solution A (1% aqueous sodium hydroxide solution) is applied to this recording paper, a heat non-sensitive part 5 permits no penetration of the coloration aid solution A and the coloration aid solution A is penetrated only in the heat-sensitive part 4 to develop a red color to make said part visible. Next, when a coloration aid B (1.5% dilute aqueous sulfuric acid solution) is acted on the recording paper, the developed color part is erased to be again brought to an invisible state. |
