| 摘要 |
PURPOSE:To obtain a letterpress plate having high durability and capable of correctly reproducing a minute character image by forming a photoresist layer on the surface of a polyimide or polyparabanic acid resin sheet, exposing the layer through an original, developing it, and etching the resin sheet with the layer as a mask. CONSTITUTION:An alkali resistant photoresist layer is formed on the surface of a polyimide or polyparabanic acid resin film, exposed to ultraviolet rays through a predetermined pattern, and developed. Using this patterned photoresist layer as a mask the resin film surface is etched with a mixed solution of NaOH, LiOH and hydrazine, and after exfoliating the layer the film is washed with water and dried to obtain a letterpress plate free from side edge with respect to shoulder angle theta of a character or a net pattern, capable of clearly reproducing halftone dots of 120 lines or more, and having superior dimensional stability, wear resistance and printing resistance. |
