PROCESS FOR MANUFACTURING A WRITING OR COLORING PENCIL BY TRI-EXTRUSION AND WRITING OR COLORING PENCIL COMPRISING AN INTERMEDIATE CASING FOR PROTECTING THE LEAD

摘要

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.