GB900963A - Improvements in or relating to leads for pencils - Google Patents

Abstract

900,963. Pencil leads. SCHWANHAUSSER, E., and SCHWANHAUSSER, G., [trading as SCHWAN-BLEISTIFT-FABRIK, SCHWANHAUSSER & CO.]. Sept. 1, 1958, No. 28016/58. Class 146 (3). A burnt pencil lead composition (i.e. one comprising basically a mixture of graphite and clay which has been fired at a high temperature) has incorporated therein one or more polar fatty substances containing two or more polar groups in the molecules thereof to improve the adhesion of the composition to smooth surfaces, the fatty substances containing, when triglyceride esters, one or more polar groups in addition to the ester groups. Such fatty substances preferably contain carboxyl, hydroxyl or amino groups and include mono- or tri- -hydroxy stearic acid or alkane triols, polydiols, e.g. derivatives of ethylene and propylene glycol, esters and ethers of polydiols, e.g. adipic acid esters, and esters of stearic acid with sorbitol, e.g. sorbitol tri-hydroxy stearate. The following examples are given :- Example I. 85 parts by weight of finest ground graphite and 15 parts of clay are shaped into rods, fired and impregnated with hydroxystearic acid or its triglyceride. Example II. 40 parts of the finest ground crystalline graphite, 15 parts of carbon black, 35 parts of the finest ground amorphous graphite and 10 parts of clay are shaped into rods, fired and impregnated with a stearic acid sorbitol ester. Example III. 85 parts of graphite end 15 parts of clay are shaped into rods, fired and impregnated with a polydiol having a molecular weight of 500-3000 and a beeswax-like consistency.