Manufacturing method of writing or coloring pencil by triple extrusion and writing or coloring pencil having intermediate coating for protecting core

摘要

According to the invention, the writing or colouring pencil is obtained by triple extrusion of three thermoplastic materials forming the "lead" material (1), the expanded "wood" material (3) and an intermediate protective layer (2) which is free of expanding agent, is compatible with the "lead" material (1) and the "wood" material (3) and has a melting point which is equal to or greater than the melting point of the "lead" material and that of the "wood" material. The three coextruded materials all contain, especially the same base component, for example a polystyrene-methacrylate copolymer. The protective layer (2) can be a different colour from the other two layers. The writing or colouring pencil with protective sheath between the "lead" and the expanded "wood", all three made from thermoplastic material, is particularly a pencil having a soft or extra-soft lead. IMAGE