Abstract: The method of continuously manufacturing pencils or crayons consists in coextruding a filled first thermoplastic material referred to as “lead” material, and around it both an intermediate “protective” layer of a thermoplastic material having no expanding agent and a second thermoplastic material containing an expanding agent and referred to as “wood” material, and in cooling said coextruded thermoplastic materials. According to the invention, the thermoplastic material constituting the protective layer is determined so that during cooling it remains deformable while the lead material shrinks. The pencil is constituted by superposing a core of a filled first thermoplastic material referred to as “lead” material, a protective layer of a non-expanded thermoplastic material, and a layer of an expanded second thermoplastic material referred to as “wood” material.

Abstract: According to the invention, the writing or coloring pencil is obtained by tri-extrusion of three thermoplastic materials forming the lead material, the expanded wood material and an intermediate protective layer, containing no expanding agent, which is compatible with the lead material and the wood material and has a melting point which is equal to or higher than the melting points of the lead material and the wood material. The three co-extruded materials all contain in particular the same basic component, such as for example a polystyrene-methacrylate copolymer. The protective layer can be of a different color from the other two layers. The writing or coloring pencil with protective casing between the lead and the expanded wood, all three being in thermoplastic material, is, in particular a pencil with soft or extra-soft lead.