| 摘要 |
PROBLEM TO BE SOLVED: To obtain a pencil core excellent in flexural strength and in the density of written lines by using a material at least containing graphite and ethylcellulose having a specified degree of ethoxyl substitution as a binder. SOLUTION: A material at least containing graphite and ethylcellulose having a degree of ethoxyl substitution of 1.5 to 2.6 as a binder is kneaded, extruded, and thermally treated to prepare a pencil core. Ethylcellulose having a degree of ethoxyl substitution of 1.5 to 2.6 is prepared by controlling the conditions in substituting OH groups of anhydrous glucose with ethoxyl groups. For example, a composition comprising 28 pts.wt. vinyl chloride resin, 2 pts.wt. ethylcellulose, 50 pts.wt. graphite, 17 pts.wt. dioctyl phthalate, 3 pts.wt. stearic acid, and 30 pts.wt. methyl ethyl ketone is kneaded with a kneader and them with a three-roll mixer, extruded into a thin wire shape, heated to 300 deg.C in air and then to 1,100 deg.C in an inert atmosphere, cooled, and impregnated with spindle oil, thus giving the pencil core.
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