WATER-ERASABLE FIRED PENCIL LEAD AND ERASION OF LINE DRAWN WITH THE SAME

摘要

PROBLEM TO BE SOLVED: To provide a water-erasable fired pencil lead and a method of erasing lines drawn therewith. ;SOLUTION: Boron nitride and an auxiliary binder for molding (an organic polymer) are kneaded, extrusion-molded and fired in a non-oxidative atmosphere to prepare the first fired lead comprising a carbide formed by carbonization of the binder and boron nitride. Then, the first fired lead is heated in an oxidative atmosphere to oxidatively remove the binder as a carbide to give a second fired lead comprising boron nitride. The second fired lead is impregnated with a perhydropoly-silazane-containing solution to fill the pores in the lead. The impregnated lead is heat-treated in an inert atmosphere to form silicon nitride whereby a third fired white lead comprising boron nitride and silicon nitride is obtained. The fired white lead is filled with a coloring composition comprising an electron-donating colorless dye, a metallic salt of a phenolic hydroxy group-bearing compound as a color developer of the dye and a nonvolatile compound desensitizing the color-developing reaction whereby the objective water-erasable fired pencil lead is obtained. The line drawn with this pencil can be erased with water.;COPYRIGHT: (C)1997,JPO