Abstract: Baked pencil leads are disclosed herein which are prepared by kneading, extruding and baking a composition containing a graphite as a filler and a binder, wherein a degree of orientation .pi. of the graphite in the direction of an extrusion axis measured by X-ray diffraction is 0.85 or more and the resultant leads have a flexural modulus of 100 GPa or more and a bending strength of 320 MPa or more. The baked pencil leads can be manufactured by carrying out the extrusion so that back face pressure just above an extrusion nozzle may be 300 kg/cm or more and a shear rate at a time when the molten kneaded composition passes through the nozzle may be 5.times.10.sup.4 (1/sec) or more.

Abstract: Baked pencil leads in which a filler such as flaky graphite is oriented in a concentric tubular form in an outer peripheral portion of each lead and which has one or more layers spaced in a radial direction from the outer peripheral portion and comprising the filler oriented in the concentric tubular form between the central portion and the outer peripheral portion of each lead and in which the filler is at random or radially oriented in the other portions of each lead. The baked pencil leads can be obtained by the use of a plurality of concentric conical tubular straightening plates having the sectional area of a flow path continuously decreased toward a nozzle orifice, in extruding a kneaded material mainly comprising the filler and a binder. In the baked pencil leads, strength can be remarkably improved without lowering density, and thus these baked pencil leads are excellent in the balance between the strength and the density.

Abstract: Baked pencil leads in which a filler such as flaky graphite is oriented in a concentric tubular form in an outer peripheral portion of each lead and which has one or more layers spaced in a radial direction from the outer peripheral portion and comprising the filler oriented in the concentric tubular form between the central portion and the outer peripheral portion of each lead and in which the filler is at random or radially oriented in the other portions of each lead.The baked pencil leads can be obtained by the use of a plurality of concentric conical tubular straightening plates having the sectional area of a flow path continuously decreased toward a nozzle orifice, in extruding a kneaded material mainly comprising the filler and a binder.In the baked pencil leads, strength can be remarkably improved without lowering density, and thus these baked pencil leads are excellent in the balance between the strength and the density.