| 摘要 |
PURPOSE:To obtain the subject product having largely improved bending strength without lowering density and having a new inner structure by extrusion molding a pencil lead material by means of a die having a current rectifying plate with a specific structure installed at an upstream side of an extrusion nozzle. CONSTITUTION:At ferst, an extender material such as graphite or carbon black and a binder preferably such as kaolinite or a vinyl chloride resin as the main components are added with a pore-forming material and they are kneaded. Subsequently, this kneaded product is extruded trough a die having pluralcurrent-rectifying plates (each 5a) at upstream side of an extrusion nozzle. This rectifying plate has a shape of a concentric cone whose cross section for current path continuously tapers toward the opening of the nozzle. In this lead core obtained by extruding through the current plate 5a and the extrusion nozzle, the extender material such as scaly graphite is oriented in the form of concentric tubes at the outer circumferential layer of the pencil lead core. The extender material formes a layer between the core part and the outer layer leaving gaps in radial direction in a concentrically oriented state. In the rest parts, an extender pigment is randomly or radially oriented. |
